The design rules can be checked for all layers, or for one layer. A
design rule check means, to check that traces/vias/pins/areafills from
different nets do not overlap each other. When a design rules check has
been executed for one or all layers, all design rule errors/warning will
be made visible.

If the board outlines consists of closed segments, and the board outline
keepout parameter is greater than zero, all the
pads/traces/vias/areafills will be checked if within these board
outlines.